Technical Field
This disclosure relates to memory devices and to protection of blocks of memory from modification.
Description of Related Art
A nonvolatile memory device such as a flash memory device can maintain stored data when not powered. Data stored in a nonvolatile memory device including an array of nonvolatile memory cells can be accessed or modified by performing read, erase, or program operations on the nonvolatile memory cells. Accidental or unauthorized changes to data stored in the device can be prevented by storing data in protected regions or sectors of the nonvolatile memory cell array. A group of nonvolatile memory cells in the device can be used to store protection bits for these sectors. Each bit indicates a protection state (e.g., protected or unprotected) for a corresponding protected sector. Software often need to switch frequently between protect/unprotect state in order to have good protection along with ease of access. However, changing the state of the nonvolatile protection bits require program/erase operations. So the protection bits only can be able to programmed/erased a limited number of times due to nonvolatile memory endurance limit. Moreover, program/erase operation of non-volatile memory requires much more operating time compared to volatile memory write operation.
It is therefore desirable to provide flexible and reliable data protection methods for storing data in a nonvolatile memory device.